Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-17-2016, 08:47 AM   #1
New Member




Join Date: Apr 2015
Location: Sioux Falls, SD, USA
Posts: 19
Trouble focusing with polarized filter

There is a full-sized bronze copy of Michelangelo's "David" that I want to photograph to 3D model.

He used to sport a handsome verdigris which also made photographing him easy. Lately the city decided to clean and wax him. While he looks great with his reflective sheen, he's a nightmare to get useful photographs for modeling.

I purchased a circular polarized lens filter and tried snapping him yesterday.

For 3D modeling photos under cloudy skies are best for outdoors items. There are no deep shadows or blown out areas to deal with and the software I use can more quickly and easily sift through the photos to build a model.

Yesterday I took a tripod and my faithful K-01 to the park, carefully adjusted the polarized filter to get rid of the reflective sheen and took my photos. It was a chilly day so I skipped pausing to check my photos until I got back to my car.

I was chagrined to find that all the photos failed to focus properly. Instead of David being in sharp focus the distant background was.

The only silver lining is that the filter did its job and dramatically reduced the sheen.

I used autofocus as I couldn't see anything of detail to manually focus once I adjusted the filter to block the shiny spots; David essentially became a dark shape on the screen.

I'm at a loss for what I did wrong. Can anyone advise me on this?

02-17-2016, 09:03 AM   #2
Loyal Site Supporter
Bengan's Avatar

Join Date: Nov 2012
Location: Stockholm
Photos: Gallery | Albums
Posts: 369
Lens used? Filter manufacturer?
02-17-2016, 09:07 AM   #3
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by jerry7171 Quote
I'm at a loss for what I did wrong. Can anyone advise me on this?
Two things you should have used:

Spot Metering.
Manual focus.
02-17-2016, 09:41 AM   #4
Veteran Member




Join Date: May 2014
Location: Linz
Photos: Albums
Posts: 301
QuoteOriginally posted by jerry7171 Quote
I used autofocus as I couldn't see anything of detail to manually focus once I adjusted the filter to block the shiny spots; David essentially became a dark shape on the screen.
That certainly is a shiny surface if it gets blocked out that much.
You could focus manually in LV and turn the filter in the right positon afterwards, altough I never had any issues with AF in combination with my polarizing filter till now.

edit:
QuoteOriginally posted by Digitalis Quote
Spot Metering.
This actually makes my advice dispensable, because the camera would meter on the statue and it should be displayed with a correct exposure in LV


Last edited by othar; 02-17-2016 at 09:48 AM.
02-17-2016, 09:52 AM   #5
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by othar Quote
the camera would meter on the statue and it should be displayed with a correct exposure in LV
...and the OP would have been able to see the statue with greater clarity, making the mis-focus more obvious.
02-17-2016, 10:09 AM   #6
Loyal Site Supporter




Join Date: Aug 2011
Photos: Albums
Posts: 1,861
what is the your polarizer filter? linear polarizer filter from old film time will affect PDAF, but I am not sure about CDAF. Try a circular polarizer filter?
02-17-2016, 10:55 AM   #7
Pentaxian
pete-tarmigan's Avatar

Join Date: Apr 2009
Location: Conception Bay South, New-fun-land
Photos: Gallery
Posts: 1,007
QuoteOriginally posted by grahame Quote
what is the your polarizer filter? linear polarizer filter from old film time will affect PDAF, but I am not sure about CDAF. Try a circular polarizer filter?
The original post says he used a circular polarizer. However, there is a possibility that it could be a linear polarizer labelled as a circular polarizer. Regardless, hasn't Pentax said that linear polarizers won't interfere with autofocus on their cameras?
02-17-2016, 11:08 AM   #8
Loyal Site Supporter




Join Date: Aug 2011
Photos: Albums
Posts: 1,861
QuoteOriginally posted by pete-tarmigan Quote
hasn't Pentax said that linear polarizers won't interfere with autofocus on their cameras?
I am not sure about that.

But in theory, light bouncing off or being transmitted the mirror will become partially linearly polarized itself (that is why polarizer filter can reduce the reflection from leaves or glass). If the light incoming is linearly polarized to started with, at some angle, the AF sensor might not get enough light - just as with light going through cross polarizers. So I am not sue how Pentax camera could be different in this aspect.

K01 does not use a mirror, and AF sensor is the same as image sensor, so it might be ok. But I have never tested it.

02-17-2016, 11:15 AM   #9
npc
Veteran Member




Join Date: Apr 2013
Posts: 311
QuoteOriginally posted by grahame Quote
what is the your polarizer filter? linear polarizer filter from old film time will affect PDAF, but I am not sure about CDAF. Try a circular polarizer filter?
This does not matter for CDAF
02-17-2016, 11:15 AM   #10
Pentaxian
pete-tarmigan's Avatar

Join Date: Apr 2009
Location: Conception Bay South, New-fun-land
Photos: Gallery
Posts: 1,007
QuoteOriginally posted by grahame Quote
I am not sure about that.

But in theory, light bouncing off or being transmitted the mirror will become partially linearly polarized itself (that is why polarizer filter can reduce the reflection from leaves or glass). If the light incoming is linearly polarized to started with, at some angle, the AF sensor might not get enough light - just as with light going through cross polarizers. So I am not sue how Pentax camera could be different in this aspect.

K01 does not use a mirror, and AF sensor is the same as image sensor, so it might be ok. But I have never tested it.
Perhaps Pentax was referring to metering not being affected, rather than autofocus.
02-21-2016, 05:01 PM   #11
Loyal Site Supporter
AggieDad's Avatar

Join Date: Jan 2015
Location: Houston, TX
Photos: Gallery
Posts: 549
This is probably patently obvious, but don't wear polaroid sunglasses when using a polarizing filter.

This happened to me when I was on my boat and had changed from my regular specs to the polaroids to cut the glare coming off the water. I never thought about it until I put my camera up to my eye.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
3d, camera, david, filter, focus, model, pentax help, photography, photos, troubleshooting, yesterday
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Trouble with DA 60-250 Focusing Accuracy (Advice Requested) jeffshaddix Pentax SLR Lens Discussion 5 01-31-2016 04:52 PM
changed focusing screen, trouble with focus... Danas_Anis Troubleshooting and Beginner Help 20 01-12-2015 11:21 AM
For Sale - Sold: Pentax DA* 50-135MM with Hoya Pro1 Digital Filter Polarized jfalcon7 Sold Items 2 11-14-2011 06:31 AM
UV filter and polarized filter mba1971 Troubleshooting and Beginner Help 7 11-09-2009 04:23 PM
Trouble with focusing indicator!? zoeybird Troubleshooting and Beginner Help 3 02-03-2009 10:52 AM



All times are GMT -7. The time now is 07:32 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top